(1) Field of the Invention
The present invention relates to a poly{1-(1-alkoxyalkoxy)-4-(1-methylethenyl)benzene} having a narrow molecular weight distribution, its preparation process, and a preparation process of poly(p-hydroxy-.alpha.-methylstyrene) having a narrow molecular weight distribution [hereinafter referred to as "poly{4-(1-methylethenyl)phenol}"].
More specifically, the present invention relates to a poly{1-(1-alkoxyalkoxy)-4-(1-methylethenyl)benzene} having a narrow molecular weight distribution, for example, a poly{1-(1-alkoxyethoxy)-4-(1-methylethenyl)benzene} or a poly{1-(2-tetrahydrofuranyloxy)-4-(1-methylethenyl)benzene} which is useful as a chemical amplification type positive resist material, and a preparation process of the polymer from industrially easily available 4-(1-methylethenyl)phenol as a starting material.
In addition, the present invention relates to a preparation process, from the above-mentioned polymer as a starting material, of poly{4-(1-methylethenyl)phenol} having a narrow molecular weight distribution which is useful, for example, as a base polymer for a chemical amplification type positive resist material.
(2) Description of the Prior Art
Poly(p-hydroxystyrene) has been noticed as a base polymer for a lithography of a high resolution or for a resist material for use in LSIs, and many preparation processes regarding the polymer have been suggested (e.g., Japanese Patent Application Laid-open Nos. 44609/1982, 199705/1988, 32832/1994 and 1115/1993).
On the other hand, poly{4-(1-methylethenyl)phenol} is more useful as compared with poly(p-hydroxystyrene), because poly{4-(1-methylethenyl)phenol} is more improved by the effect of a methyl group on the .alpha.-position than poly(p-hydroxystyrene) in performances such as a dissolution rate in a resist removal step with a release agent and a plasma resistance in a dry etching step which are required as the resist material applicable to a high integration. However, a polymerization method of poly{4-(1-methylethenyl)phenol} is limited by electronic and steric influences of the methyl group on the .alpha.-position, and hence a preparation method of poly(p-hydroxystyrene) cannot directly be applied as it is.
In fact, the present inventors applied some of typical methods disclosed as the preparation method of poly(p-hydroxystyrene) to the preparation of poly{4-(1-methylethenyl)phenol}.
For example, in accordance with a method described in Japanese Patent Application Laid-open No. 32832/1994, an anionic polymerization of p-t-butoxycarbonyloxy-.alpha.-methylstyrene was tried at -78.degree. C. in the presence of n-butyl lithium as a polymerization initiator in tetrahydrofuran, but a reaction between a t-butoxycarbonyloxy group and n-butyl lithium predominantly occurred, so that the desired polymer could scarcely be obtained.
Furthermore, in accordance with a method described in Japanese Patent Application Laid-open No. 1115/1993, an anionic polymerization of p-tetrahydropyranyloxy-.alpha.-methylstyrene was tried at -78.degree. C. for 1 hour in the presence of n-butyl lithium as a polymerization initiator in tetrahydrofuran, but a polymerization reaction scarcely proceeded, so that the desired polymer could not be obtained.
However, there have been suggested some methods by which these difficulties can be solved and poly{4-(1-methylethenyl)phenol} can be manufactured.
Japanese Patent Application Laid-open No. 179204/1986 has disclosed a method which comprises subjecting an esterified compound of p-hydroxy-.alpha.-methylstyrene to a cationic polymerization in the presence of antimony pentahalide as a catalyst to form a polymer, and then hydrolyzing the polymer to obtain poly{4-(1-methylethenyl)phenol}. In this cationic polymerization, however, methanol or water is used as a polymerization terminator, and therefore, a terminal of thus obtained poly{4-(1-methylethenyl)phenol} should be a methoxy group or a hydroxy group. As just described, the functional group naturally bonds to the polymer terminal, so that resistance to thermal decomposition deteriorates. For this reason, the thus obtained poly{4-(1-methylethenyl)phenol} is not preferable as a base polymer for a resist material which is required to be heated in a lithography step.
In Makromol. Chem., Macromol. Symp., Vol. 53, p. 139-149 (1992), there has been disclosed a method which comprises subjecting p-tert-butoxycarbonyloxy-.alpha.-methylstyrene to a cationic polymerization in the presence of a boron trifluoride ether adduct as a catalyst in a sulfur dioxide solvent to form poly(p-tert-butoxycarbonyloxy-.alpha.-methylstyrene), and then heating this compound at about 200.degree. C. to obtain poly{4-(1-methylethenyl)phenol}.
However, since similarly utilizing the cationic polymerization, this method also has the same drawback as described above. In addition, the molecular weight distribution of the polymer obtained by this method is relatively broad, that is, 2.4 to 4.6, and it is not preferable as a resist material in this point.
Japanese Patent Application Laid-open No. 199705/1984 has disclosed a method which comprises reacting p-bromo-.alpha.-methylstyrene with magnesium in an ether, further reacting it with peroxybenzoic acid 1,1-dimethylpropyl ester in tetrahydrofuran to obtain p-1,1-dimethylpropoxy-.alpha.-methylstyrene, subjecting this compound to an anionic polymerization, and then carrying out an acid decomposition to obtain poly{4-(1-methylethenyl)phenol}. However, this method employs a Grignard reaction, and an equimolar or more magnesium is necessary, and the handling of secondarily produced magnesium bromide is troublesome. Accordingly, the disclosed method is not considered to be a practical method.
In Japanese Patent Application Laid-open No. 32819/1994, there has been disclosed a method which comprises subjecting methoxymethoxy-.alpha.-methylstyrene to a living anionic polymerization, and then eliminating a methoxymethoxy group to obtain poly{4-(1-methylethenyl)phenol}. However, in this method, in order to synthesize methoxymethoxy-.alpha.-methylstyrene which is a starting material, an expensive chloromethyl methyl ether is necessary. In addition, an equimolar alkali metal chloride is formed as a by-product, and hence the treatment of this by-product is also required. Accordingly, this method is not considered to be an industrial manufacturing method.
As described above, an efficient preparation method of poly{4-(1-methylethenyl)phenol} has not been present so far, and hence it has riot been industrially used.
On the other hand, a poly{1-(1-alkoxyalkoxy)-4-(1-methylethenyl)benzene} is considered to be useful as a chemical amplification type positive resist material having a high sensitivity, a high resolution and a high plasma resistance in a dry etching step.
As conventional techniques, typical preparation methods of only a related poly{1-(1-alkoxyethoxy)-4-ethenylbenzene} have been present as follows.
(1) A method which comprises reacting p-bromophenol with an alkyl vinyl ether to obtain a p-bromo(1-alkoxyethoxy)benzene, reacting this compound with metallic magnesium, carrying out a Grignard reaction between the reaction product and vinyl bromide in the presence of dichloro{1,2-bis(diphenylphosphino)ethane}nickel as a catalyst to obtain a p-(1-alkoxyethoxy)styrene, and then adding 2,2'-azobisisobutyronitrile as an initiator to the reaction system to carry out a radical polymerization, thereby preparing the desired product (Japanese Patent Application Laid-open Nos. 194842/1994 and 249682/1993).
(2) A method which comprises adding 2,2'-azobisisobutyronitrile as an initiator to p-tert-butoxystyrene to carry out a radical polymerization and to thereby obtain poly(p-tert-butoxystyrene), eliminating a tert-butoxy group by concentrated hydrochloric acid to obtain poly(p-hydroxystyrene), and then reacting this compound with an alkyl vinyl ether to prepare the desired product (Japanese Patent Application Laid-open No. 319155/1995).
However, these methods cannot provide any polymer having a narrow molecular weight distribution, and therefore, the products obtained by these conventional methods are poor as chemical amplification type positive resist materials in which a high resolution is required.
Of these methods, the method (1) comprises first changing a phenolic hydroxyl group of p-bromophenol as the starting material into an alkoxyethoxy group, carrying out the Grignard reaction, and then conducting the radical polymerization. Therefore, this method has many reaction steps, and in the Grignard reaction, the expensive catalyst having a phosphine ligand is used. Thus, the recovery and reuse of this catalyst is indispensable, which makes the process more complex. In addition, the secondary production of a large amount of magnesium bromide causes one problem, and hence, the method (1) cannot be considered to be an industrial preparation method of the poly{1-(1-alkoxyethoxy)-4-ethenylbenzene}.
Moreover, in the method (2), poly(p-hydroxystyrene) is first obtained, and the alkoxyethoxy compound is then formed. However, owing to the reaction with the polymer, it is difficult to sufficiently carry out the reaction with the alkyl vinyl ether, and the obtain product is a copolymer of a p-(1-alkoxyethoxy)styrene and p-hydroxystyrene. In consequence, a homopolymer of a 1-(1-alkoxyethoxy)-4-ethenylbenzene cannot be obtained.
Furthermore, it is known that the related poly{1-(2-tetrahydrofuranyloxy)-4-ethenylbenzene} is useful as a chemical amplification type positive resist material having a high sensitivity, a high resolution and a high plasma resistance in a dry etching step, and also useful as a starting material for the preparation of p-hydroxystyrene polymer by eliminating a part or all of 2-tetrahydrofuranyloxy groups from the polymer [Journal of Applied Polymer Science, Vol. 42, p. 877-883 (1991) and Polym. Mater. Sci. Eng., Vol. 61, p. 417-421 (1989)].
It is also known that the tetrahydrofuranyloxy group has higher acid decomposition properties as compared with the tetrahydropyranyloxy group, and hence the compound having the tetrahydrofuranyloxy group is useful as the resist material.
As a preparation process of this poly{1-(2-tetrahydrofuranyloxy)-4-ethenylbenzene}, there has been disclosed a method which comprises reacting p-hydroxybenzaldehyde with 2,3-dihydrofuran in the presence of an acid to obtain p-dihydrofuranyloxybenzaldehyde, carrying out a Wittig reaction between this compound and (bromomethyl)triphenylsulfonium bromide in the presence of tert-butoxy potassium to obtain 1-(2-tetrahydrofuranyloxy)-4-ethenylbenzene, and then subjecting this compound to a radical polymerization in the presence of azoisobutyronitrile as a polymerization initiator to prepare the desired product.
However, this method cannot provide the polymer having a narrow molecular weight distribution, and therefore, the product obtained by this method is poor as a chemical amplification type positive resist material in which a high resolution is required. Moreover, in a lithography step, there is a drawback that a dissolution rate in a resist removal with a release agent is too high.
In this preparation method, p-hydroxybenzaldehyde is used as a starting material, and a phenolic hydroxyl group is first changed into a tetrahydrofuranyloxy group, followed by the Wittig reaction and the radical polymerization. However, this method has many reaction steps and so it is complex, and during the Wittig reaction, an expensive phosphonium salt is changed into phosphine oxide, so that many by-products are formed and their handling is difficult. In consequence, this method is not practical as the preparation method of poly{1-(2-tetrahydrofuranyloxy)-4-ethenylbenzene}.
On the other hand, 4-(1-methylethenyl)phenol (popular name: p-hydroxy-.alpha.-methylstyrene) can be easily obtained by the thermal decomposition of 2,2-bis(4'-oxyphenyl)propane (popular name: bisphenol A) (Japanese Patent Publication 52886/1981).
Thus, the present inventors have presumed that if a poly{1-(1-alkoxyalkoxy)-4-(1-methylethenyl)benzene} having a narrow molecular weight distribution, for example, a poly{1-(1-alkoxyethoxy)-4-(1-methylethenyl)benzene} or a poly{1-(2-tetrahydrofuranyloxy)-4-(1-methylethenyl)benzene} can be easily prepared from an industrially easily available 4-(1-methylethenyl)phenol as a starting material, the thus prepared polymer can be utilized as a polymer which is useful as a chemical amplification type positive resist material, and from this polymer, poly{4-(1-methylethenyl)phenol} having a narrow molecular weight distribution which is useful as a base polymer for the resist material can be prepared. Accordingly, the present inventors have intensively investigated with the intention of realizing these presumptions.
As a result, it has been found that (1) a poly{1-(1-alkoxyethoxy)-4-(1-methylethenyl)benzene} having an optional molecular weight and a narrow molecular weight distribution can be easily prepared in a high yield by reacting 4-(1-methylethenyl)phenol with an alkyl vinyl ether to form an alkoxyethoxy compound, and then subjecting this compound to an anionic polymerization; (2) a poly{1-(2-tetrahydrofuranyloxy)-4-(1-methylethenyl)benzene} having an optional molecular weight and a narrow molecular weight distribution can be easily prepared in a high yield by reacting 4-(1-methylethenyl)phenol with a dihydrofuran to form a tetrahydrofuranyloxy compound, and then subjecting this compound to an anionic polymerization; and (3) poly{4-(1-methylethenyl)phenol} having an optional molecular weight and a narrow molecular weight distribution can be easily prepared in a high yield by reacting the above-mentioned polymer with a protonic acid in the presence of an organic solvent. In consequence, the present invention has been attained.